1. Field of the Invention
The present invention relates to a technique for reading data from a disk of a hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads can magnetize and sense the magnetic fields of the disks to write and read data, respectively. The heads are coupled to a pivoting actuator arm that has a voice coil motor.
Data is typically stored on tracks that extend radially across the disk surfaces. The voice coil motor can be energized to pivot the actuator arm and move the heads to different track locations. Each track is typically divided into a number of sectors. Each sector contains at least one data field.
Data is read from the disks in accordance with a read operation controlled by the disk drive controller. The read operation typically includes enabling a read gate of a read channel. Enabling the read gate causes the heads to sense the magnetic fields of the disks. If the drive is unsuccessful in reading the data, the controller will retry the read operation in accordance with a retry step from a retry look-up table. The retry look-up table typically contains a sequence of retry steps. Each retry step may utilize different head parameters. For example, the read current and cut-off frequency of the head may be changed for each step.
The disk drive will continue to retry the read operations in accordance with the retry steps until data is successfully read from the disk, or the drive has tried all of the retry steps in the table. The retry technique does not always insure a successful read of data. It would be desirable to improve the quality of the retry technique to capture accurate data.